There are two types of “Documents & Data” stored on iPhone and iPad, both of which can take up space on a device. One is usually app specific caches and other related app data, and the other is iCloud related files for an app. The fact they share the same name but have different functions, and are references in different sections of iOS Settings, is a little confusing, but they are different.

The “Documents & Data” associated with an iOS app include things like caches, app data, preferences, login details, and assorted other app-specific information. Most of this data is expendable and in many situations for many apps that have large Documents & Data storage consumption, the data tends to be very heavy on caches. This is typically the type of Documents and Data on an iPhone or iPad that users want to remove to free up some space.
The simplest way to delete Documents & Data on an iPhone or iPad is by removing the app and then re-downloading it again. That may not make a lot of sense, but for the time being Apple offers no method in iOS to manually delete caches and app data, so instead if you want to delete that app data, you have to delete the app entirely.
Keep in mind that when you delete an app, and then re-download it, you will likely lose whatever data (game levels), logins, and other saved details from that app. Do not do this if you don’t have login information saved elsewhere, and do not delete an app or its documents and data caches if you have important data stored within that app. You should back up your iOS device before beginning so that you can restore in the event you mess something up.
1 Open the “Settings” app in iOS
2 Go to “General” and then go to “Storage & iCloud Usage”
3 Go to “Manage Storage” under the ‘Storage’ section
4 Find the application(s) that have the ‘Documents & Data’ you want to delete (for example, Twitter is a 64MB app but can often take up several hundred MB with its Documents and Data), then tap on that app and choose “Delete App”
5 Now go to the “App Store” and search for and re-download the app you just deleted
6 After the app has finished re-downloading, if you return to the same Storage screen you will find it now consumes much less space because the documents and data has been cleared out

(keep in mind that deleting and redownloading an app also will update it to the latest version available, so don’t do this if you want to keep using an older version of an iOS app)